The long-term goals of this research effort are to elucidate the molecular mechanisms leading to the overexpression of the mdm2 oncogene and to define the role that such overexpression plays in pathways of tumorigenesis. The mdm2 oncogene has transforming activity that can be activated by overexpression, and is frequently amplified in human tumor cells. Proteins encoded by the mdm2 oncogene can bind to, and inhibit the function of, two key tumor suppressor proteins, p53 and RB. Dr. George has identified a number of human tumor cell lines that express very high levels of both mdm2 proteins and a stabilized, wild type p53 protein. This unanticipated combination may represent a new scenario of transformation involving these genes. New data also indicate that the more than 50 fold overexpression of the mdm2 proteins in these cells is associated with enhanced translation. This mechanism has not previously been implicated in the regulation of mdm2 gene expression, and it represents a novel means by which the potential transforming activity of the mdm2 oncogene could be activated. The investigator has outlined experimental approaches to better define the molecular and cellular mechanisms governing the complex regulation of the mdm2 gene, as well as its role in mediating the process of cellular transformation. Building on an initial analysis of the altered mdm2 and p53 expression in these tumor cells, a framework has been developed to begin to dissect what may be a fundamental pathway of transformation. Toward that goal, the specific aims include: (1) Elucidate the mechanism of mdm2 translational control in the tumor cells, and determine if it is directly related to, or reliant on, the aberrant p53 expression; (2) Characterize more fully the physiological status, and interactions, of the mdm2 and p53 gene products in these tumor cells; (3) Test the prediction that overexpression of mdm2 in these tumors inhibits normal RB function, contributing to altered proliferation controls; (4) Determine if the stabilized p53 has an altered cellular location or transcriptional activation potential. These studies promise to provide new insights into mechanisms of cellular transformation, and ultimately lead to more effective diagnosis and therapy of human cancers.